First result of a google on the Vendor:DeviceID is the Linuxant HSF (softmodem) driver page. As I recall from trying to use Linuxant drivers on an internal modem in a laptop years ago it was quite a painful experience, but could be made to work. I hope things have improved since those bad old days. The license still appears to be rather restrictive which probably explains the lack of packages in the usual repos.

Thank you for kindly response.Unfortunately I couldn't install driver for that external modem.

I prepared an internal modem "Z_Cyber" and after I typed "Yum update", its driver installed .I typed "lspci" and found the following :Communication controller:conexant system ,INC, HCF 56 K Data/Fax/Voice SPKP modem (worldwide) (14f1:1056)

My question is, how can I change its' setting ? Thank you very much for any help

It would seem some confusion was introduced about the internal Conexant modem and the external D-Link modem the thread started with, which would be serially attached.Not having used a modem for a long time, and not at all on Linux, I'd expect that external modem to be addressed through the serial port it is attached to. Whatever application uses that modem should allow for port and baud-rate selection, after which the modem would be controlled through its AT-command set. No driver required, at least not for the modem. I expect the serial port driver to be part of CentOS.